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-   -   bouyantBoussinesqSimpleFoam continuity error (http://www.cfd-online.com/Forums/openfoam-solving/105665-bouyantboussinesqsimplefoam-continuity-error.html)

Mojtaba.a August 6, 2012 05:48

bouyantBoussinesqSimpleFoam continuity error
 
Quote:

SIMPLE: convergence criteria
field p_rgh tolerance 0.01
field U tolerance 0.0001
field T tolerance 0.01
field "(k|epsilon|omega)" tolerance 0.001


Starting time loop

Time = 1

DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0169481, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.0186144, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 0.0176119, No Iterations 1
DILUPBiCG: Solving for T, Initial residual = 1, Final residual = 0.0291332, No Iterations 1


--> FOAM FATAL ERROR:
Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 2.05531
Specified mass inflow : 0.529467
Specified mass outflow : 0
Adjustable mass outflow : 1.82776e-17


From function adjustPhi(surfaceScalarField& phi, const volVectorField& U,const volScalarField& p
in file cfdTools/general/adjustPhi/adjustPhi.C at line 116.

FOAM exiting
p
Quote:

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
wall
{
type zeroGradient;
}

air-inlet
{
type zeroGradient;
}

out_flow
{
type fixedValue;
value uniform 0.9;
}
}
U
Quote:

internalField uniform (0 0 0);

boundaryField
{
wall
{
type fixedValue;
value uniform (0 0 0);
}

air-inlet
{
type fixedValue;
value uniform (0 -1 0);
}

out_flow
{
type zeroGradient;
}
}
What is the problem?
Regards

Mojtaba.a August 6, 2012 06:15

I just solved the problem. I hadn't worked with potentialFoam.
I know it was a stupid question. But for those who are beginner in openFOAM like me:
1) make a copy of your current case
2) use potentialFoam to run the case. in this step you initialize your values.
3) copy 0/U file into your own case.
4) start solving.

best ~

adambarfi April 20, 2013 01:23

hi everybody,

I have the same problem. first, I ran potentialFoam and it says that no continuity error exists. then I changed the solver to buoyantBoussinesqSimpleFoam and ran it. but the following error appeared agian:

Code:

[1] --> FOAM FATAL ERROR:
[1] Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux              : 0.0582779
Specified mass inflow  : 1.08721e-09
Specified mass outflow  : 0
Adjustable mass outflow : 0
[1]
[1]
[1]    From function adjustPhi(surfaceScalarField& phi, const volVectorField& U,const volScalarField& p
[1]    in file cfdTools/general/adjustPhi/adjustPhi.C at line 118.
[1]
FOAM parallel run exiting
[1]


my U bcs:
Code:

dimensions      [0 1 -1 0 0 0 0];

internalField  uniform (0 0 0);

boundaryField
{
    fixedWalls
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    openW
    {
        type            zeroGradient;
    }
    hot
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    fb
    {
        type            empty;
    }
}


my p bcs:
Code:

dimensions      [0 2 -2 0 0 0 0];

internalField  uniform 0;

boundaryField
{
    hot
    {
        type            fixedValue;
        value          uniform 0;
    }

    openW
    {
        type            fixedValue;
        value          uniform 0;
    }

    fixedWalls
    {
        type            fixedValue;
        value          uniform 0;
    }
    fb
    {
        type            empty;
    }
}

anybody knows what should I do?

thanks a lot
Mostafa

adambarfi April 20, 2013 01:57

hi again,
it seems my problem was solved!!!!
I changed my zeroGradient velocity BC to fixedValue and waited to openFoam solved it in some iterations, then I changed it to zeroGradient again. there is no continuity error :D

I think the reason is when a model is solved by BCs different from the original BCs, actually the results are used as the initialize values for the next run. do I right????:confused:

adambarfi April 20, 2013 11:12

NO, It didn't work. this way fixed my BC as fixedValue.

when I ran the potentialFoam the following results appeared:
Code:

Create time

Create mesh for time = 0

Reading field p

Reading field U


Calculating potential flow
DICPCG:  Solving for p, Initial residual = 0, Final residual = 0, No Iterations 0
DICPCG:  Solving for p, Initial residual = 0, Final residual = 0, No Iterations 0
continuity error = 0
Interpolated U error = 0
ExecutionTime = 5.27 s  ClockTime = 5 s

End

I think there is a problem, it added the phi but it didn't change my BCs.

please help me

Mojtaba.a April 20, 2013 12:25

Quote:

Originally Posted by adambarfi (Post 421886)
hi everybody,

I have the same problem. first, I ran potentialFoam and it says that no continuity error exists. then I changed the solver to buoyantBoussinesqSimpleFoam and ran it. but the following error appeared agian:
.
.
.

thanks a lot
Mostafa

Dear Mostafa,
You do not have any velocity inlet or pressure inlet in order to make your case work.
after defining a velocity inlet, I prefer to use zeroGradient BC for walls and inflow, and a fixed Value 0 BC for outflow in pressure dictionary.

adambarfi April 20, 2013 12:56

thank you, Mojtaba

I have solved this case before, with this difference that the recent geometry is longer than later geometry. I increased grid number but the error was appeared, but when I decrease it, it worked. already I'm running it. I hope it return correct results.
but I don't understand why this error appears?????

thanks again.
Mostafa

Mojtaba.a April 20, 2013 13:01

Quote:

Originally Posted by adambarfi (Post 421991)
with this difference that the recent geometry is longer than later geometry

What do you mean by this?
You mean by decreasing number of grids you are able to run the case, but increasing it, causes the error?

adambarfi April 20, 2013 14:59

yes, I think when I increase the grids the cumulative continuity error increases, while the grids are decreased this error decrease also.


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